It is highly desirable to transmit ultrasonic energy into gases to be able to analyze the gases for their composition, flow and other properties and to conduct remote and level sensing of objects through air. It is also highly desirable to transmit ultrasonic energy into air to perform non-contact testing upon products, such as paper, wood, low acoustic impedance green ceramics and powder metals, plastics and composites as well as high acoustic impedance ceramics, metals, etc. In medical applications, it is also highly desirable to conduct non-contact diagnostics of skin and other parts of the body of humans or animals, fetus monitoring, blood flow measurements, and for non-contact and non-invasive therapeutical and surgical applications, such as for malignant skin removal, lipotirpsy, unwanted mole removal, etc. It is also highly desirable in agricultural applications, such as for plant and tree diagnostics, as well as for fruit, vegetable and seed analysis.
It is well understood that the acoustic impedance of gases is several orders of magnitude from the acoustic impedance of typical piezoelectric materials. Also, the larger the difference in acoustic impedance of two adjacent layers, the more difficult it is to transmit ultrasonic energy across the boundary between the two layers. Finally, it is known that gases rapidly absorb ultrasonic energy especially as the frequency of the ultrasound is increased.
It has been possible with a certain degree of success to transmit ultrasound into gases, such as air, by placing a low impedance material in front of the piezoelectric element. The transmission of ultrasound into gases has nevertheless been far less than desired.
It is an advantage, according to this invention, to provide a greatly improved ultrasonic transducer and method of using same which transmits ultrasonic energy into gases with much greater efficiency.